A composite or laminated type organic photosensitive material has been developed and put to practical use in recent years. This type of organic photosensitive material is disclosed in, for example, Japanese Patent Publications Nos. 42380/1980 and 34099/1985. It comprises an electroconductive support, a charge producing layer and a charge transporting layer formed on the support. For instance, such a composite photosensitive material has an electroconductive support of aluminum layer deposited on a polyester film, a charge producing layer formed on the aluminum layer, and a charge transporting layer formed on the charge producing layer.
The charge producing layer is formed by, for example, preparing a dispersion of a charge producing substance together with an organic solvent, a binder resin, and if necessary a plasticizer, applying the dispersion onto the support, and drying to a thin film. The charge transporting layer is formed by, for example, dissolving a charge transporting substance in an organic solvent together with a binder resin, and if required a plasticizer, applying the solution onto the charge producing layer, and drying to a thin film.
It is generally accepted that copy images produced with such a laminated photosensitive material as above mentioned by a discharged area developing electrophotographic process often contain image defects such as dark spots or lines thereon. Thus, it is already known that the provision of an undercoat composed of a resin between the electro-conductive support and the charge producing layer to obviate the problem of such image defects.
Accordingly, it is necessary that the undercoat prevents the injection of electric charges into the photosensitive material from the electroconductive support so that the photosensitive material is stably electrified thereby to eliminate the defects on the copy images. It is also necessary that residual potential is not accumulated on the material so that the photosensitive material provides clear images after a long term use. The use of an alcohol soluble polyamide resin has been proposed to form an undercoat to meet those requisites, as disclosed in Japanese Patent Publication No. 58-45707 and Japanese Patent Application Laid-open No. 60-168157.
As above set forth, there have been proposed a variety of improvements in the laminated photosensitive material, however, not a few important problems remain unsolved. One of such problems is that a copy image produced by such a laminated photosensitive material contains interference fringe-like unevenness in darkness thereon.